Many dental procedures require the dentist to form an impression of patients' teeth, either alone or in conjunction with the gums and vestibular anatomy. This impression typically is either used directly by the dentist to analyze the patient's mouth structure or is used to form a plaster replica of the patient's teeth, gums, and vestibule. Such impressions are typically used to produce dental replacement components and dental assemblies such as crowns, teeth, bridgework, dentures and other oral prostheses.
Dental impression trays for obtaining an impression of a patient's dentition are well known. Such trays generally include tray portions anatomically contoured to fit at least a part of a patient's upper and/or lower oral anatomy, of which an impression is to be obtained. An appropriate impression material is placed in the tray and inserted in the mouth. After the impression material sets, it is used as a mold, into which plaster or dental stone can be poured which upon setting forms a model of the patient's oral anatomy. In addition, the set impression material may also be used directly as a mold for other purposes such as the fabrication of temporary restorations, the process of teeth whitening etc.
Dentists use trays to carry impression material to the mouth and to support the moldable material intra-orally until it cures. The design of the tray depends on the size and shape of the area to be recorded. Tray sets typically include variably-sized upper and lower troughs, each filled with impression material such as a settable material. The upper impression corresponds to an impression section of maxilla, the lower impression corresponds to a complimentary section of mandible, and the two complimentary impressions jointly provide an impression of the bite relationship of mandible to maxilla.
Metal trays are typically used for the above-mentioned procedures. Metal trays are expensive. They require cleaning and sterilization before reuse, which is inconvenient. In the process of obtaining any impression, called the modeling process, dental trays to contain the impression materials are used, and such dental impression trays are generally classified into ready-made (stock) trays and customized trays. In order to obtain more exact impression, customized trays fitted on an individual are manufactured from the model made by using the ready-made trays. So, ready-made trays could be regarded as one of the most basic apparatus for manufacturing an exact restoration. The arch has the shape of a horse hoof formed by person's teeth and alveolar bones, and its size and shape differs from person to person. A set of ready-made dental impression trays usually comprises at least 4 maxillary trays (small, medium, large and extra large) and at least 3 mandibular trays (small, medium and large). However, these conventional ready-made trays are so complex that even an expert has some difficulty in selecting and classifying them, and furthermore, there are some cases that none of such ready-made trays fits an individual. It is, therefore, difficult to obtain an exact impression through conventional ready-made trays.
Current disposable trays are inexpensive, which gives them the convenience of disposability. However, their flexibility and plastic memory can cause intra-oral distortions in the impression. The lack of complete rigidity in a plastic tray can create a “springback” distortion transfer from the tray to the impression material on release of pressure to the tray sides, which is inadvertently applied by hard- and soft-tissue interferences at some point during the impression-making process. For example, pressure can be generated by the tongue, by occlusal forces pushing material against the tray wall, by the cheeks, or by tray impingement of gingival tissues, alveolar ridge, retromolar pad, tuberosity and teeth. This pressure flexes the tray while the impression material sets, causing inaccuracies in the impression when the distorted tray attempts to return to its original shape upon removal from the mouth. An impression in a flexible frame can also be distorted by forces applied to remove the tray from the patient's mouth or during routine laboratory handling. These inaccuracies are then transferred to the master cast when it is made in the dental laboratory.
The use of thermoplastics in the field of dentistry is known. Conventionally, hardened or semi-hardened thermoplastics are used in the making of dental impressions, for example. Thermoplastics are also used as material to build up regions of castings that serve as the basis for making dentures. In order to melt or soften thermoplastics in the conventional dental office or laboratory, a dedicated water bath, which may be a so-called crock pot, such as found in the domestic kitchens, has been used to soften the thermoplastic. Alternatively, it has been known to heat up a cup of water in a microwave oven to a temperature of 150.degree. F. or more, and then carry the hot cup of water into the room where the dentist or technician is working the thermoplastic material. Currently in the dental field thermoplastic is typically used in the form of pre-formed wafers, such as so-called TEMP-TABS™, which are heated in use. There is also known thermoplastic which is incorporated in a triple tray or dental impression tray, such as a so-called THERMO-TRAY™. Both the TEMP-TABS™ and the THERMO-TRAY™ must be softened in hot water, as discussed above. This heating in the dental office not only leads to the problems discussed above, but if the thermoplastic is improperly overheated, it may develop undesirable bubbles. Further, the TEMP-TABS™ are very costly and, even if a relatively small quantity of TEMP-TABS™ is required for a procedure, such may be cost prohibitive.
Unformed thermoplastic is a relatively inexpensive material. Needless to say, such prior art devices and methods of heating and using heated thermoplastic material are impractical, if not unwieldy.
What is needed is a new tray system that will fit any patient during any clinical situation using any impression making technique that is required. What is also needed is a tray system that is universal and easy to use by clinicians.